NED Abstract

Copyright by American Astronomical Society.
Reproduced by permission
2005ApJ...625..763L
The Molecular Interstellar Medium of Dwarf Galaxies on Kiloparsec Scales:
A New Survey for CO in Northern, IRAS-detected Dwarf Galaxies
A. Leroy, A. D. Bolatto, J. D. Simon, and L. Blitz
Abstract. We present a new survey for CO in dwarf galaxies using the ARO
Kitt Peak 12 m telescope. This survey consists of observations of the
central regions of 121 northern dwarfs with IRAS detections and no known CO
emission. We detect CO in 28 of these galaxies and marginally detect
another 16, increasing by about 50% the number of such galaxies known to
have significant CO emission. The galaxies we detect are comparable in
stellar and dynamical mass to the Large Magellanic Cloud, although somewhat
brighter in CO and fainter in the far-IR. Within dwarfs, we find that the
CO luminosity L_CO_ is most strongly correlated with the K-band and the
far-infrared luminosities. There are also strong correlations with the
radio continuum (RC) and B-band luminosities and linear diameter.
Conversely, we find that far-IR dust temperature is a poor predictor of CO
emission within the dwarfs alone, although a good predictor of normalized
CO content among a larger sample of galaxies. We suggest that L_CO_ and
L_K_ correlate well because the stellar component of a galaxy dominates the
midplane gravitational field and thus sets the pressure and density of the
atomic gas, which control the formation of H_2_ from H i. We compare our
sample with more massive galaxies and find that dwarfs and large galaxies
obey the same relationship between CO and the 1.4 GHz RC surface
brightness. This relationship is well described by a Schmidt law with
{SIGMA}_RC_ is proportional to {SIGMA}^1.3^_CO_. Therefore, dwarf galaxies
and large spirals exhibit the same relationship between molecular gas and
star formation rate (SFR). We find that this result is robust to moderate
changes in the RC-to-SFR and CO-to-H_2_ conversion factors. Our data appear
to be inconsistent with large (order of magnitude) variations in the
CO-to-H_2_ conversion factor in the star-forming molecular gas.
Keywords: Galaxies: Dwarf, Galaxies: ISM, ISM: Molecules, Stars: Formation